A . A home pregnancy test is 97% accurate if taken a week or more after the missed period, so it sounds as though your negative test should be accurate. A blood test can tell if you are pregnant as soon as 7 days after conception and a doctor's urine pregnancy test can tell if you are pregnant around when you next period should come. Often, not having a period can signal that you are not ovulating. Reasons for this include: medications such as birth control pills, stress, excessive dieting, excessive exercise, or a hormone imbalance such as with a thyroid disorder or polycystic ovarian syndrome. If you continue to miss your period or to have an irregular cycle, give your doctor a call. Good luck!